Pendulum inclinometer for sighting instruments



Oct. 2, 1951 R. o. BROWNING PENDULUM INCLINOMETER FOR SIGHTING INSTRUMENTS 2 Sheets-Sheet l [NVN To? @fameuse/v 0. Bean/NW6 "Oct 2, 1951 R, o, BROWN|NG 2,569,796

PENDULUM INCLINOMETER FOR SIGHTING INSTRUMENTS Filed June 16, 1945 2 Sheets-Sheet 2 ,92 [NVE/vra@ cHneoso/v Q BevwN/N@ HWP/g K/ECH, Fs rf@ @HARP/s TTOPNE V5 Patented Oct. 2, 17951 UNITED STATES PATENT OFFICE PENDULUM IN CLINOMETER FOR SIGHTING INSTRUMENTS 7 Claims.`

My invention relates in general to measuring instruments and, more specifically, to an instrument whose operation is characterized by the necessity for establishing a reference line which is oriented in a predetermined direction. This requirement may be satisfied by the provision of an instrument, or a component of an instrument, which is adapted for establishing the reference line when the instrument, or the component thereof, assumes a predetermined position.

Measuring devices of this general character Which require the establishment of a reference line for operation thereof may include, for example, such instruments as transits, levels, sextants, etc. The operation of such instruments necessitates the establishment of a reference line which ordinarily is oriented horizontally or vertically relative to a reference plane, although intermediate orientations may also be employed. The reference plane may, for example, be a plane which traverses the center of the earth and will be considered as such herein for the `purpose of disclosing the invention. The measuring instrument preferably includes a movable component which is adapted for assuming the predetermined position in response to the action of a suitable motivating agent.

For the purpose of disclosing the invention, I prefer to consider an application of the fundamental concepts thereof to an exemplary embodiment which is known in the art as a sextant. Conventional sextants include a movable component which is adapted for assuming a vertical position in response to the gravitational attraction of the earth, whereupon the reference line will lie in a vertical plane traversing the center of the earth. Many conventional sextants include a sighting tube through which an observation of a star, or other heavenly body, may be made, the movable component being pivotable relative to the sighting tube. When the movable component assumes a vertical position relative to the earth because of the action of gravity, the angle of elevation of the star may be indicated by a suitable scale. Some conventional sextants require that the angle of elevation be read by an operator while the observation is being made, an obviously unsatisfactory procedure particularly if the sextant is employed aboard a marine vessel, aircraft or any other unstable observation point. Other conventional sextants are provided with manually operable means for latching the movable component relative to the sighting tube when the observation has been made and the angle of elevation may thereafter be read with greater facility. The latter type of conventional sextant is subject to similar disadvantages in that simultaneous observation of a star and latching of the movable component are extremely difficult operations to perform with any degree of accuracy and are particularly difficult when an unstable observation point is ernployed. Furthermore, the results obtained from all such conventional sextants are subject to the inaccuracies inherent in human judgment, since the vertical position of the movable component must be determined by the estimate of the operator.

In view of the foregoing considerations. a primary objective ofl my invention is the provision of a measuring instrument which includes an automatic means for indicating to an operator thereof that the predetermined orientation of the aforesaid reference line has been established. As applied to the exemplary embodiment of my invention, the foregoing primary objective includes the provision of an automatic means for indicating that the movable component of the sextant has assumed a vertical position or orientation. Ahother primary objective is to provide i a means for recording the position of the movable component automatically when the latter assumes the predetermined position. The recording means may include means for interrupting the motion of and `securing the movable component automatically when the latter assumes the predetermined position. In the preferred embodiment described hereinafter the datum recorded is the angular variance of the line of sight of the instrument from the perpendicular, as evidenced by the position of the pendulum in relationship to the quadrant of the sextant.

I prefer to effect a realization of the foregoing primary objectives by means of the aforesaid exemplary embodiment with no intention of limiting the scope of my invention thereto. The exemplary embodiment is intended as a means for disclosing the fundamental concepts of my invention, the latter being susceptible to incorporation in various other embodiments vby those proficient in the art.

The sextant preferably includes a means for defining a line of sight which is pivotally attached to a frame to permit vertical orientation of the frame in response to the action of' gravity. A movable component in the form Aof a pendulum means is pivotally attached to the frame and is adapted for angular `motion relative to the frame in response to the gravitati-onal attraction of the earth.

In accordance with the primary objective of my invention, I contemplate the provision of means for recording the position of the pendulum relative to the frame automatically when the pendulum assumes the predetermined position. The recording means preferably includes means for interrupting the angular motionofthe pendulum automatically when the latter assumes the predetermined position, the position preferably being vertical relative to the earth. The interirupting means includes a means for-. secur-ingthe pendulum to the frame and includes Ya' means f o r l5 actuating the securing means automaticallywhen the pendulum assumes the desired-position.v Thew aforesaid actuating means is preferablyadapted for automatic operation in response to the actionV l#relationship between the index and the line of Sieht, I I may-.be employed.

'V Th'e' foregoing components of the sextant may be operated in the conventional manner by mak- -:fingran-observation-fof-'a star, or any other object,

with the lineof sight defining means I0, the latter preferably including a conventional sighting of gravity when the pendulum assumesithe-desired position and the preyision thereof is an objective of my invention.;.Y

The` actuating meansis .preieraloly -electrical and includes a eirouithavinggvariable .characteriSticS, aiiotloerY objective of. my, invelotionl being to.

provide. a vgravity responsive. means .for` varying the eliaracteristicsof .tnecircuit automatically the pendulum moves aneularlyalooutsthe point of pivotal attachment .thereof to effect automatic actuation .of the, securing meant .when the pendulum ie vertical..Tl1.e .liaraeteiisticeof theeir-` cuit maybe varieelloy employiuaa. circuit which iS Vuouiuilly open'eravity ieepousivefmeans being provided for. closingv the circuit. .automatically when the pendulum assumes a vertical position. The latter function preieraolylperformed by a gravity responsive neither-revision there.- of is a further object vepimy invention.

: The .foregoing and .various otheirobiectivee and. advantages o f my invention,may-begattained by means of thefafcresaiel.exemplary eine.oellmeiit` thereof whichis describedinthe following dis'- closure and shown in theacompanying draw? ings7 jvvhieh are. .merely` ier .illustrative purposes,- wherein:

Fig. 1 is aV side. elevationalffvievv ci the -eX- emplary embodiments of my inventiomj Fig. 2 is a sectional View taken as indicatedby the broken line.2.-2 o f Fi g 1;

Fig. 3 is a eeetionalyievvtalseu alongthe broken. line 3-3 of Fig. 1;

Fie. 4 is a sectional view., taleilaeiudicated by the broken line 4-.4 of Fig. 2, illustrating the secured position ofthe aforesaid means` forsecuring the pendulum means to the frame;

Fig. 5 is a sectional View similar toV Fig.` .4. illustrating the unsecured position ofthe Asecuring means;

Fig. 6 is a sectional Vview-,j talgen as indicatedby the line 6--6 of Fig. 2, illustrating the aforesaid gravity responsive, circuitclosing means;r and Fig'. 7 is a Wiring diagram illustrating a suitable electrical circuit. Y

Referring to .the drawings, the sextant includes a means I0 for defining-a line. of silght which is indicated by thedotted line II, -the means I0 being pivotally attached to a frame I2 by coaxial pivots I3 and I4 whose .axes are substantially parallel to the line of sight II. lI-he axesof the pivots I3 and I4 need not beparallel to the lineof sight II, however, and any desired relationship may be employed. A pendulum means I6, which includes a mass, or bob YI'I and a supporting member, orv rod I8, ispivotally attached to the Yframe I2 by a pivot I9, the axisiof theH latter being'. perpendicular to the.. axes of.l the tubev or telescope, having suitable peep holes, crosshairs, or the like vtherein (not shown) for defining; the. linefcisigl-it. lli, makingftheeobservation, an.; operator ofthe sextautzsuppoyts the latter by; the Sighting. vrtube I0, thus. permittine angular*moticuoirthefframelzfpaigallel.- toa; primary planewhich.isperpendi-eularfto tliefaXesoi lthe frame pivotSJ-S and lkandrparallel .togthe axis of the pendulum-.pivot yl :Tile pivot lafpeifmits Simultaneous .angular motion. of the pendu.- lum I6 parallel to a;,seondary, plana whichgis perpendicularto .the primary plane.. Whena oondition of static equilibrium is'attained, tlieirarne.

I2 and pendulum. I6 assume vertical. DOStionsand the Secondary plancfandtherefeieuce line .deiiiied bytliepointers. 2| valso become veitieal.-Y The anele on the Scale22.indieatedloyithe .pointers .211. represents the angle cielevationfof the-flinefcf,

sight I I relative to thei'iori z ontal,Y

It will be apparentgthat if theobservationis made from an unstable observationipointfeuch as` from an oceanfgoing vesseL; Yan aircraft, or the like, a staticv equilibrium condition. may be irnpossible to achieve. encountered if an observationis; attempted from a Windy observation point. The operator ofthe sextant must relyk upon his own-.judgment inqdef. termining the precise instant. when both; thel frame. I 2 and penduluml GlareverticallyeorientedL a task which requires .a skill-fuloperator even` under favorable-.conditions.Y

In view. of these considerations, VLprefer tiefemploy. an automatic means-frm` determiningatne Vprecise moment when b,oth the frarneAZ and Vpendulum I6 'are verticallydisposed, For :the

purpose of simplifyingthe disclosure.; the. assump-V will be understood, howeyer, 'tnatth to be described may .alsdbeV adapted.

after.

VIn general,

posed includes means :Z4- for .recordingtthe `position of thependulum.- I5 relativefto the. frame I2 ,g the means-24 being` adapted forfinterrupting'ithefangular motion of Vthe;pendu-lum llgin-,gthegexem-f plary embodiment'illustrated. The

includesa means-21 for actuatingjtliegseeur means 26 automatically. when thel pendulum assumes a predetermined-position;"Thezactuat meansZl includes nelectrical Icu1tr2lif;- iii-normally open.audfipelueleeiarayi Similar diiiicoltiee may. be

the automatic apparatus.: forde terf.Yy mining when the pendulum I-6.;is.ve rtic llyfdisg ,teifruptingf means 24. generallyilllvlldeS-amwN-F2155.forts@ curing the peruiulumv I6: ton-the frame l2:

as ccf/ecA means 29 and 3| for closing the circuit 28 automatically at the proper moment.

Referringparticularly to Figs. 2, 4, and 5, the securing means 26 is mounted on the pendulum bob |1 and includes a plunger 32 which is reciprocably disposed in a bore 33 in the bob I1. The upper end of the plunger 32 is provided with a bore 34 within which is inserted the stem 36 of a frame-engaging element 31, the latter having a groove 38 therein which is adapted to receive the arcuate edge 39 of the frame I2 to interrupt the angular motion of the pendulum I6 about the pivot I9. The lower end of the plunger 32, which is provided with an annular flange 4| thereon, extends into a counterbore 42 in the bob I1 through a bore 43 in an insert 44, the latter being threadedly connected to a tubular sleeve 46 which is disposed in the counterbore 42. The annular flange 4| on the plunger 32 is reciprocable within a bore 41 inthe tubular sleeve 46 and is adapted for engagement with the actuating means 21 through an opening 49 in the tubular sleeve 46 as will be described in detail hereinafter. The lower end of the plunger 32 is engaged by the head 49 of a second plunger 5I the latter being reciprocable within the bore `i1 in the tubular sleeve 46. The frame engaging element 31 is adapted for being urged into engagement with the edge 39 of the frame I2 by means of a spring 52 which encloses the stem 53 of the plunger 5I and is seated against the head 49 thereof, the other end of the spring 52 being seated against an insert 54 which is secured in the bore 41 in the tubular sleeve 46. The lower end of the sleeve 46 is provided with a iiange 56 thereon which is secured to the bob I1 by a screw 56. The lower end of the stem 53 of the plunger 5| depends from the bob I1 and is secured to a member 58 having a knob 59 thereon to permit downward displacement of the plunger 5I by the operator of the sextant.

The securing means 26 is normally retained in the position illustrated in Fig. 5 by the actuating means 21 which will be described hereinafter. When the pendulum I6 assumes a vertical position, the actuatingl means 21 automatically releases the plunger 32 whereupon the spring 52 urges the frame engaging element 31 into engagement with the frame I2 to interrupt the angular motion of the pendulum I6 relative thereto. The various components of the securing means 26 are then disposed as illustrated in Fig. 4. The pendulum I6 may be released relative to the frame I2 by the simple expedient of exerting a sufficient downward force on the knob 59 to compress the spring 52 whereupon the actuating means 21 again engages the securing means 26 as illustrated in Fig. 5.

The actuating means 21 includes a latching member 6| which is pivotally attached to the bob |1 by a screw 62, the latching member 6| being provided with arms 63 and 64. The arm 63 extends through the opening 48 in the tubular sleeve 46 into engagement with the annular flange 4| on the frame engaging plunger 32. The arm 64 is pivotally attached to a member 66 which is slidably disposed in a slot 61 in the bob I1, the latching member 6| being urged into the position illustrated in Fig. 5 by a relatively light spring 68 which is secured to the arm 64 and the bob I1. The slidable member 66 is provided with a notch 69 therein which is adapted to receive a locking member 1|, the latter being disposed in a slot 12 which communicates with the slot 61. The locking member 1| is attached to a projection 6. 13 on an armature 14j by ,apivotl 16 which is disposed in an elongated opening 1]," the armature 14 being pivotally attached to the bob I1 at 1 8. The locking member 1| is urged into engagement with the slidable member 66 by a relatively light spring 19 which is secured to an end 8| ofthe armature 14 and to theA bob I1. The armature 14 is disposed adjacent the core 82 of an electromagnet 83, the latter being energizable automatically by current flowing, through conductors v 84 and 86, which form part of the electrical circuit 29,- When the pendulum I6 assumes a vertical position as will be described hereinafter.

When the electromagnet 83 is energized, the armature 14 is attracted to the core 82 as illustrated `in Fig. 4, the` magnetic attraction being suiiicient to overcome the relatively light spring 19. The locking member 1I simultaneously disengages the slidable member 66, thereby permitting the latching` member 6I to rotate about the pivot 62 and release the securing means 26, as illustrated in Fig. 4, whereupon the latter interrupts the angular motion of the pendulum I6 as previously described. The spring 52 which urges the securing means 26 into engagement with the frame I2 issuficiently heavy to overcome the relatively lightspring 68 which normally urges the arm 63 of the latching member 6| into engagement with the flange 4| on the frame engaging plunger 32. `When the engagement of the securing means 26 with the frame |2 is terminated as previously described and the electromagnet 83 is de-energized, the: spring 68 urges the latching member 6I into engagement with the flange 4| of the `plunger 32 and the spring 19 acts on the armature 14 to urge the locking member 1| into engagement with the slidable member 66, thus latching the securing means 26 in the position illustrated in Fig. 5'.

Referring particularly to Fig. '1, the electrical circuit 28 includes a primary circuit 81 and a secondary circuit 88, both of which are normally open. YVThe primary circuit 81 includes the electromagnet 83 and conductors 84 and 86 which were described previously. The conductor 84 is connected to the armature 89 of a relay 9| having a core 92, the armature 89 being attracted by the core 92 whenever the relay 9| is energized as will be described in detail hereinafter. The armature 69 acts as a switch in the primary circuit 91 and is adapted for engagement with a contact 93 to close the primary circuit 81 when the relay 9| is energized. The contact 93 is connected to a conductor 94 which is `in turn connected to a group of batteries 96 and 96a, the latter being connected in series. A conductor 91 is connected to the group of batteries 96 and 96a and to a manually operable switch 98 which is in turn connected to the conductor 86.

It will be apparent that whenever the secondary circuit 88 is energized and the switch 98 is closed, the electromagnet 83 will be energized and will actuate the securing means 26 to interrupt angular motion of the pendulum I6 as previously described. f The relay 9|, which is part of the secondary circuit 88, is connected to the battery 96a by a conductor 99 and to the gravity responsive circuit closing means 29 by a conductor IUI. A conductor |62 interconnects the gravity responsive circuit closing means 29 and 3|, the latter means 3| being connected to the battery 96a by a conductor |03.

`In the exemplary embodiment illustrated. the batteries 96 and 96a and the relay 9| are mounted in va suitable case |04 (shown in phan- 7A tom) Landare connected to the vsextantv'byfa cable I 06f' which includes the conductors- 84'; 91,l 0| and `r|03 as best Sl'mWnirr-Fig; 1. v-"-I-lfzecables-I 06 is preferably suiciently long to permit'- considerable -movement ofY the operator' -relative-VY to the case |04 for-vconvenience-fin` usingwthetsextant.

Thefmanuallyoperablenswitch 98 --may-be 'convene' ien-tly mounted on the'sighting Ntubefl Il as-shQWn inFlig. l.

` The gravityresponsive-circuit'closingv means-291 and 3 I, Ywhich will -be= described hereinafterfare mounted on thependulum-bobY andi lare adapted to close the A'secondary4 circuit 881` whenv the pendulum I6 assumes-avertical position, thusenergizing -thev relay-- 9| i 'fThelatter `closes the-primary circuit-81;thusfenergizing theJ elec tromagnet 83 Jand-causing th'eactuatinglf means- 2l =to actuatetheiseeuring means 2B-as@ previously described.. The switehf--98f-prevents I`Vvactuation-oiv the securing-means 26 until -lthezoperatorf of the seXtantihas-completed his-observation of a star, or otheri object. -Actuation ofvthey securing means 26 isthusprevented bytheopenswitcn 98iuntil the operator Otthe--SeXtant--feels thatlafsatisfactory.4 observation lhas :been made.

VReferring particularly to Fig 6, the; gravitylresponsiveVV circuit closing --means or vgravityl -re spons-ive switch-i3 I1 includes l a-f housing- I Gl [into which l extendA primary and `secondary contacts I 08 and (19, respectively-,f :the-primary-V contact I 081- being connected /tovthe VVccnflductor |02 -Y and the secondary con-tact Y'I 09 toithe conductor UI 03. Thehousi-ng `|01is:partially-filledwithaf-lluidI I I to submerge theesecondary-feontact `|09 beneath the surface thereof, th'e -iluid A|||'-prei-era'bly beingar conductonof feleetricitynsuchas mercury. Anf electrical conductor` 2 is supportedby-or floats -on the mercury Land: is Lprovidediwith Y a pair rof vprojections-I Iii-andAVV [|f4lthereon', the project-ion; I-I3 being' adapted Vforvengagement Withthe'primarycontact-IBB.- The projectionk I |l|= pivotallyengages-1a rod 2 I I 6 which extends 1in-tothe housing l' |31 intermediate l the L ends:- ot f the` oating conductor I I 2;

@Asbestshownin Figs.-- land 2, 'thee gravity responsiveA switchl is provided lwithv bands fl whichfencircle the housing-I 3-1 and-are--prefer ably separated therefrom v`byipads H85' Thef-encirclingfbands 5 I are secured to '-a-'supportin'gmember 9 .by-screws -|2 l; the supportingmem ber' IIS being` attachedtoai-mountingemember |22 Vby a 1 leaf spr-ingA |-23lfwhichis secured by screws |211.` VThe mounting-memberA '|22 isi at` tache'df tof the-pendulum bob f I'libyV screws |25' and is provided with an ladjust-ingserevvff-'IZT' therethrough 'which' is i adapted for engagement with the supporting member I I3 tofeffectfadjust;V ment of the position1of@theegravity 'responsiveI switch 3 I relativetothe'bobf-I 1 ,-suchf' adjustment being permitted by the-'leaf spring 231 The function-of the adjusting"screwr |21Tis-tofvvary-:the position of the' gravity 'responsive switchl 3| f'so ||2 engages thev'primary -contact-GB-when'the pendulum f I@ assumes'a --vertical position.v

YIt Willfbe apparent thatas'the'pendulumiI6'V is Adisplaced angularly in one direction,r the'loat# ing conductor; ||f2-v/-ill engage the-primaryvconethe opposite direction, 'theoating conductor?- H21' Wm disengage,v :the .'.primaryvcontact |118 :to fopen theY sWitchSrl.. As indicatedbiini-Eig. FT, thefcon-i.

struction offthevgravity aresponsivesswitch. .-29'i's1;

identical tofflthat of 'thefswitch 3I except that the orientation thereof '1 relativeV to vthe bob I 'Iltis reversed,-the axes ofrotation 'of"=the-oating conductors I| 2 of both-'switches 29 :and 3l-nbeing substantially parallelf'to the aXisof rotation of f the pendu-lum! I 6 abouti -the-pivot1- I 9. It=Will be-apparentfthatif the-pendulum |6is displaced angularlyfin one Ydirection from =the Vvertical, the switch=2 Bfwi'll Ebe Y openVI andv the switch 3 I Will lbe closed, andfif -thefpendulurn` I6 is displacedin the'opposite direction, the reverse Will-obtain.- Bothf switches :2 9 landfi3 I ivvill-be-closed only when the pendulum '1| lassumesa vertical position-and since-thesWitches--ZS and 3| areconnectedin series by the conductor IGZ; 'the secondaryfcin cuit''willbe closedonly.y when such afvertical position isfassumed byfthependulum I6.

When the secondary circuit 38 1 is closed in this manner and the manuallyv operable switch -98 inthe primary circuitY 81 is closed bythe "operator Of'theseXtant, the'actuating means-21A will'actuate the lsecuring means 26 to secure the pendulum `I6 relative Vto the *frame I2 automati cally; The-angle of 'elevation of the line of sight I may then be determined readily and accuratelyf by f means of thel reerence pointers 2| VVand scale 22.V

Considering-the actual 'case Vwherein `theirame I2 is not vertically disposed'lat all times andz'is free-tomove angula-rly-"about the pivots |31and I4 an additional lpair Y of gravity responsive switchesinot shown) maybe attached-tothe pendulum bob |'I andconnected in series with the switches 29-and '3|; The additional 'switches should -be mounted with the axes of rotation-of the Viloating conductors Ythereof substantially perpendicular i to the-1axis A'of rotation of theY pen-- dulum.V I5" about the pivot 19j "The additional switches thus will be perpendicular to -ftheV switches 293 and "3|, thereby permittingactuation of the securing meansfZ-Ef only when -b'oth theframe |2'and pendulum Bl'are verticallydisposed. lIf desired,- however, the sextantmay be employed WithonlythesWitches`29 Yand'3| in operation, lit-'tl'ienbeing necessary for the 0perator tode'terminewhenthe frame |2is ver'- tical by estimate.

Instead of employing the conductivaproperf ties of--theffiuidfl lifor Ieffecting electrical cornmun-ication between`A` the` secondary i contact I' l|l9`- and oating fconductor l2Y as f previously; dis'-V cussedf-thealternativeconstruction illustratediin Fig.l 6 Arnay'fb'e employed. (The housing |31 "of, thegravityresponsivesv/'itchI 3 iis provide'zdiwith` an encirclingfband |128 through which is thread-'1 and the iioati'ng'l conductorA I 2 .'is `thus vefected by 'rneans 'fof fthe: projection |4- andpivot rod 6; the op'erationwf of "the .alternative construc-v tionV being` similar tozithatpreviouslyniscussed; In *this con'struetiom Ith'eifluid I .I need not abe a` conductor 'of f'electricity.

Fromfthe foregoing: con'sideratrons,.it` will b'e apparentthatthe securing `means r2651Wi1l be actuated :by Vthe actuatingf.means-2'| to vsecure the lpendulumf-'I fto `the xframe VI2 .automatically Whenwthe rpendulum 6: assumesl a Vvertical .position andy/hen thelnanually operable switch V98 Y is closed.. Thus, -inamaking-.an observation, the

operatorfofathe fsextant merelycloses the switch" f'lwhen a:satisfactoryobservationrismadeV and Y y `needf'maintain': theiobservationfonly;longenoushi observation vuntil a condition of static equilibrium of the vpendulum I6 is attained. My invention thus appreciably shortens the length of time required for making` an observation and materially increases the accuracy thereof since the indication is obtained automatically before the pendulum I6 comes to rest or becomes static. As previously indicated, additional gravity responsive switches may be connected in series with the switches 29 and 3| to prevent closure of the secondary component 88 of the electrical circuit 28 until both the frame I2 and pendulum I6 assume vertical positions.

The sextant may be employed to make an observation from an unstable point with facility and with a high degree of accuracy. Since maintenance of the observation until static equilibrium of the frame I2 and pendulum I6 is attained is unnecessary, the operator of the sextant will not tire as rapidly as when employing conventional sextants wherein maintenance of the observation until equilibrium is attained is essential. The shorter observation time thus materially improves the accuracy of the observation in view of the fact that the operator may tend to Waver when making a lengthy observation. All guesswork regarding the position of the frame I2 and pendulum IB is eliminated by the automatic operation of the securing means 26.

It will be understood that the position of the pendulum I E relative to the frame I2 may be recorded in various manners and need not be limited to the means 24 forinterrupting the angular motion of the pendulum IB when the latter assumes a predetermined position. For example, the plunger 32 of the securing means 26 may be adapted to make the scale 22 at the proper moment instead of securing the pendulum I6 to the frame I2. The pendulum bob I'I may also be provided with a camera (not shown) which is adapted for actuation by the actuating means 21 to photograph the scale 22 automatically when the pendulum I6 assumes a predetermined position.

Although I have described an exemplary embodiment of my invention wherein the fundamental concepts thereof are applied to a sextant, I have no intention of being limited to the specic disclosures contained herein since the fundamental concepts of my invention are susceptible to incorporation in various other embodiments by those procient in the art; I hereby reserve the right, therefore, to the protection oiered by the full scope of my appended claims.

I claim as my invention:

1. In an instrument, the combination of: sighting means; pendulum means pivotally mounted on and adapted for angular motion relative to said sighting means; means for recording the position of said pendulum means relative to said sighting means; and means carried by said pendulum means for actuating said recording means automatically when said pendulum means assumes a predetermined orientation.

2. In a measuring instrument, the combination of: sighting means; a frame pivotally connected to said sighting means; a pendulum pivotally attached to said frame and adapted f or angular motion relative thereto; means for recording the position of vsaid pendulum relative to 'when said pendulum assumes `10 said frame; and means carried by said pendulum for actuating said recording means automatically a predetermined orientation.

\ 3. In a device for measuring inclination from the horizontal, the combination of: sighting means frame means pivotally connected to said lsightingmeans on a frame axis parallel to the axis of said sighting means, said frame means 'including an arcuate scale; pendulum means piv- .fotally connected to said frame means and adapted to rotate in alignment with said scale; and means for automatically stopping movement of said pendulum means relative to said scale when said pendulum means attains a vertical position.

4. In a device for measuring inclination from the horizontal, the combination of sighting means; frame means pivotally connected to said sighting means on a frame axis parallel to the axis of said sighting means, said frame means including an arcuate scale; pendulum means pivotally connected to said frame means on a transverse axis normal to said frame axis and adapted to rotate in alignment with said scale; and means for automatically stopping movement of said pendulum means relative to said scale when said pendulum means attains a vertical position.

5. In an instrument for measuring vertical angies, the combination of: frame means; pendulum means pivotally connected to said frame means for angular motion relative thereto; recording means including an element connected to and movable with said pendulum means and including a co-operating element connected to said frame means for recording angular positions of said pendulum means relative to said frame means; and gravity responsivemeans connected to and movable with said pendulum means for actuating said recording means automatically when said pendulum means assumes a predetermined orientation.

6. An instrument according to claim 5 wherein said recording means includes resilient means for biasing one of said elements toward an operative position to record the angular position of said pendulum means relative to said frame means, and includes electrically operable means for releasing said one element, said gravity responsive means including a gravity responsive switch which is connected in series with said electrically operable means and which closes automatically when said pendulum means assumes said predetermined orientation.

'7. An instrument as set forth in claim 5 including sighting means connected to said frame means for establishing a line of sight perpendicular to the axis of angular motion of said pendulum means.

RICHARDSON O. BROWNING.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 204,133 Chandler May 28, 1878 '783 612 Clark Feb. 28, 1905 973.909 Benson Oct. 25, 1910 1,152,701 Barresen Sept. 7, 1915 1,308,795 McCormack July 8, 1919 1,314,258 Fisher Aug. 26, 1919 1,393,318 Saxton Oct. 11, 1921 (Other references on following page) .-Name. Date Rail Apr. \=19,5:192'7 Sperry Jan..f1`3,ff19;3;-l Shaknazaror Sept. L15, 1931 Schoolcraft Feb.xf16, 1932 Gilbert Mar.- 29;:'1932 Inglis Apr. 524,' :133.4

Hegenberger- Feb; 25, .21936 *Inglis* Jangllyfl Craig Feb. ;18,f194$1 

